Being a cook, I try to keep my kitchen stocked with a variety of stuff.
For veggies, I always try to have onions, ginger, fresh herbs, tomatoes, potatoes, carrots, celery, mushrooms, and garlic on hand. Often have green beans, broccoli, peppers (hot and mild), and/or asparagus around too. Also depends what's in season and looks good at the market.
For fruit, I always try to have apples, bananas, lemons, limes, and oranges around. I love getting other types of fruit (mangoes, pineapple, strawberries, etc), but it all depends on what's in season and how fresh it is.
For protein, I try to have some form of beef and chicken on hand. Sometimes I'll get some good pork or some lamb as well. I'm a big fan of seafood, so I do buy a lot of fish and shellfish (usually cook it the day I buy it since it doesn't keep very long). Currently I've got some nice salmon steaks that were on sale, and I'm going to cook tomorrow.
I always try to have a supply of rices (jasmine, arborio, etc), pastas (straight noodles, shaped noodles, etc), bread crumbs (homemade unless they're panko), oils (olive, sesame, peanut, canola, etc), vinegars (balsamic, red wine, sherry, apple cider, etc), spices (dried herbs, salts, peppers, cumin, etc), and bread (baguettes, Cuban, dinner rolls, burger buns, etc).
Also try to have milk, heavy cream, orange juice, eggs, and a few different kinds of cheeses (cheddar, parmigiano-reggiano, brie, etc) on hand as well.
That's not including some other stuff I buy that either looks good or is on sale (currently have a huge watermelon on my counter for instance
).
Edit: I forgot alcohol. I always try to have a twelve pack on hand as well as a bottle of wine to cook with. Also, I sometimes buy some hard liquor (both for cooking and pleasure
).